1. Field of the Invention
The present invention relates to a laser welding apparatus. More specifically, the present invention relates to a laser welding apparatus to carry out laser welding with a laser beam radiated after the laser beam enters a diffractive optical element (DOE).
2. Description of Related Art
Laser welding using a laser beam is carried out for joining plural members into a single welded structural body. An example of productions joined by such laser welding may include batteries. In general, batteries are configured to include electrode bodies formed of positive and negative electrode plates inside cases. In a producing process of such batteries, after the electrode bodies are housed inside case bodies from openings thereof, a joining step to seal the openings of the case bodies with sealing plates, and then joining the case body and the sealing plates together by laser welding is carried out in some cases. In the joining step, the laser welding is carried out along welding lines at position where the openings of the case bodies and side surfaces of the sealing plates face each other.
For example, Japanese Patent Application Publication No. 2013-220462 describes a technique to join a case body and a sealing plate together by irradiating a welding line between the case body and the sealing plate with a low-density laser beam having a lower power density and high-density laser beams each having a higher power density than the low-density laser beam. In JP 2013-220462 A, while both the case body and the sealing plate are broadly irradiated with the low-density laser beam, the high-density laser beams are radiated such that spots of the high-density laser beams are located within a spot of the low-density laser beam. The aforementioned low-density laser beam and high-density laser beams are embodied by beam-formation of a single laser beam with a DOE. After the temperature is increased to some extent by the low-density laser beam, the high-density laser beams can be applied. Through this configuration, it is possible to prevent rapid increase in temperature at an irradiated portion with the high-density laser beams, thereby preventing bumping or the like at the welded portion. Subsequently, the low-density laser beam is applied to the irradiated portion irradiated with the high-density laser beams. Through this configuration, it is possible to prevent rapid decrease in temperature at the irradiated portion with the high-density laser beam, thus suppressing generation of cracks or the like. It is described that, accordingly, it is possible to suppress generation of welding defects.
In laser welding, it is preferable to carry out a more flexible control depending on the condition of joint target portions, or in order to form a desired joined portion in a shorter time.